The disclosure of Japanese Patent Application No. 2000-388740 filed on Dec. 21, 2000, including the specification, drawings and abstract, are incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to engine valve drive control apparatus and method for controlling driving of engine valves of an internal combustion engine based on electromagnetic force generated by electromagnets.
2. Description of Related Art
Valve drive apparatuses for driving engine valves, such as intake valves and exhaust valves, of internal combustion engines by use of electromagnetic force of electromagnets, have been known. The valve drive apparatus of this type is desired to ensure a high operating stability when driving the engine valves. Furthermore, it is desirable to minimize the amount of electric power that is consumed for driving the engine valves, and to suppress occurrence of noises when the engine valve reaches either one of the opposite ends of its stroke (or a range of its displacement), namely, the fully closed position or the fully open position.
In a known apparatus as disclosed in Japanese Patent Laid-open Publication No. 9-217859, the actual operating state of the engine valve is detected, and the electromagnetic force generated by a selected one of the electromagnets is controlled so that the actual operating state coincides with a target operating state of the valve. In this manner, the electromagnetic force of the electromagnet is controlled to a magnitude that meets various requirements as mentioned above.
When controlling the electromagnetic force generated by the electromagnet, the apparatus as disclosed in the above-identified publication operates to determine, for example, a displacement deviation between an actual displacement of the engine valve and a target displacement thereof, and apply a controlled current to the selected electromagnet so that the resulting electromagnetic force has a magnitude suitable for making the actual displacement of the engine valve equal to the target displacement thereof. If the displacement deviation is large, for example, the exciting current applied to the electromagnet is increased so that the engine valve is opened or closed with accordingly increased electromagnetic force.
It is, however, advisable to note that the engine valves are subjected to external forces generated in accordance with the internal pressure within a corresponding combustion chamber of the engine, the intake pressure or the exhaust pressure, and the like. If the relationship between the external forces and the target operating state, such as a target displacement, is not appropriate, namely, if the target displacement is determined without taking account of the current magnitude of the external force, the exciting current applied to the electromagnet may be excessively increased, resulting in an increase in the power consumption or occurrence of noises upon opening or closing of the engine valve. In other cases, the electromagnetic force for driving the engine valve may be short of the required force for driving the engine valve, resulting in a reduction in the operating stability of the engine valve.
If a pattern of the target displacement with respect to time is set so as to meet the above-described various requirements under a condition that the external force applied to the engine valve is relatively small, the actual displacement does not follow the pattern of the target displacement when the external force applied to the engine valve is relatively large since the displacement velocity (driving velocity) of the engine valve is reduced with an increase in the external force. In this case, an excessively large current may be applied to the selected electromagnet, resulting in an increased amount of power consumption and noises occurring upon opening and closing of the valve. If a pattern of the target displacement with time is set so as to meet the above-described various requirements under a condition that the external force applied to the engine valve is relatively large, on the other hand, the displacement velocity of the engine valve is increased when the external force applied to the engine valve is relatively small, and therefore the exciting current applied to the electromagnet is reduced so as to reduce or restrict the displacement of the engine valve. As a result, the electromagnetic force generated by the electromagnet may fall short of the required force for driving the engine valve, resulting in a deteriorated operating stability of the engine valve.
It is therefore a first object of the invention to provide a control apparatus for controlling driving of an engine valve, which apparatus permits the engine valve to operate with a sufficiently high operating stability irrespective of the external force applied to the engine valve, while at the same time avoiding an increase in the electric power consumed for driving the valve and/or occurrence of noise upon opening and closing of the valve.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention a drive control apparatus for controlling driving of an engine valve of an internal combustion engine, utilizing an electromagnetic force generated by at least one electromagnet. A controller of the apparatus estimates a magnitude of an external force applied to the engine valve, and sets a target operating state of the engine valve in view of the estimated magnitude of the external force. Then, current applied to the electromagnet(s) is controlled in accordance with an actual operating state and the target operating state of the engine valve, so that the actual operating state substantially coincides with the target operating state.
The drive control apparatus constructed as described above is able to appropriately set the target operating state of the engine valve in accordance with the external force applied to the valve, so as to achieve a desirable opening or closing action of the engine valve. By controlling current applied to a selected electromagnet so that the actual operating state of the engine valve coincides with the target operating state, therefore, the control apparatus permits the engine valve to be driven with an appropriate electromagnetic force that varies depending upon the external force. Accordingly, the engine valve is operated with a sufficiently high operating stability without suffering from a lack or shortage of electromagnetic force required for driving the engine valve. Furthermore, the engine valve is prevented from being driven with excessively large electromagnetic force, which would result in an increase in the amount of power consumption and/or occurrence of noise and vibrations upon opening and closing of the valve.
Here, the operating state of the engine valve may be represented by a driving velocity or a displacement of the engine valve.
In one preferred embodiment of the invention, the control units calculates a feedback current having a current value that varies with a deviation of the actual operating state from the target operating state, and controls the current applied to the electromagnet(s), based on the calculated feedback current.
With the above-described arrangement, the feedback current used for energization control of the selected electromagnet for driving the engine valve is calculated so that the actual operating state of the engine valve substantially coincides with the target operating state that is set in view of the external force applied to the engine valve. By controlling current applied to the selected electromagnet based on the thus calculated feedback current, the drive control apparatus is able to drive the engine valve with a suitably controlled electromagnetic force corresponding to the external force, thereby suppressing or avoiding various problems that would otherwise be caused by excessively small or large electromagnetic force.
In the above-indicated preferred embodiment of the invention, the control unit may set a feedback gain used when calculating the feedback current, such that the feedback gain increases as an air gap between the engine valve and a selected one of the electromagnets increases.
The electromagnetic force applied to the engine valve varies depending upon the size of the air gap between the engine valve and the selected one of the electromagnets. Namely, assuming that the same exciting current is applied to the electromagnet, the electromagnetic force acting on the engine valve decreases with an increase in the air gap. In the above arrangement in which the feedback gain is set to a greater value as the air gap increases, the electromagnet is able to generate electromagnetic force of a magnitude that is suitable or appropriate for the size of the air gap, so that the actual operating state of the engine valve can be controlled with high reliability to the target operating state within a sufficiently short time.
In another preferred embodiment of the invention, the control unit sets a feed-forward current having a current value that is added to the feedback current so as to make the actual operating state substantially equal to the target operating state, and controls the current applied to the at least one electromagnet, based on the feed-forward current and the feedback current.
In the above embodiment, feed-forward control based on feed-forward current, as well as the above-indicated feedback control, is performed during control of current applied to the selected electromagnet, so that the actual operating state of the engine valve coincides with the target operating state thereof. Accordingly, the control of the current applied to the electromagnet can be accomplished without a time delay.
In a further preferred embodiment of the invention, the estimating unit estimates the magnitude of the external force based on the actual operating state of the engine valve that is detected while the at least one electromagnet is held in a non-energized state in which no current is applied to the engine valve.
With the above arrangement, there is no need to provide a new sensor for estimating the external force acting on the engine valve.